It is well known that the traction of vehicles on soft terrain may be greatly improved by decreasing the pressure within the tires. By decreasing the pressure, the tire supporting surface will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desirable to decrease the tire pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth roads thereby increasing economy and safety.
It would be desirable to be able to adjust the pressure within the tires without having to stop the vehicle and manually inflate or deflate the tires. This is especially true for military vehicles which usually travel in columns, many times under conditions whereby stoppage of the vehicle would delay the entire column. Additionally, if the military vehicle is under enemy attack it is imperative that the vehicle maintain its maneuverability for as long as possible. If a tire has been punctured by gunfire or the like it is necessary to be able to at least partially inflate the tires very quickly so that the vehicle remains usable.
Various automatic tire inflation systems have been used in the past to alleviate one or more of these problems. One such system was standard equipment on U.S. Army vehicles known as the "Duk" which were used in World War II. This technique used a so-called Schrader valve system in which air pressure was supplied through long wand-like conduits which protruded from the vehicle wheel openings in the frame and fed air into rotating couplings connected to the exterior of the hubs. A second line from the inboard edge of the rotating couplings were connected to the valve stems in the inner tubes for the tires.
One of the problems with this approach was its extreme vulnerability to damage since the conduits which carried the air were exposed to the rough terrain over which the vehicles passed. The conduits were subject to being broken or damaged by coming into contact with brush, rocks, or other vehicles.
In an attempt to improve upon this system there have been several reported attempts to provide an internal air pressure feed technique that would not be subject to such abuse. It is believed that some of the vehicles used in the U.S.S.R. and its satellite countries have used automatic tire inflation systems in which air from a compressed air source is routed through the wheel assembly and into the tire. Additionally, the following U.S. Patents form a representative, but not exhaustive, list of various other approaches to automatic tire inflation systems: U.S. Pat. No. 2,693,841 to Webster, Jr.; U.S. Pat. Nos. 2,944,579 and 2,976,906 to Kamm et al; U.S. Pat. Nos. 2,634,783 and 2,634,782 to Turek et al; U.S. Pat. No. 2,577,458 to Gaiptman; U.S. Pat. No. 2,849,047 to Lamont et al; U.S. Pat. No. 3,362,452 to Harnish; U.S. Pat. No. 1,800,780 to Daneel; U.S. Pat. No. 3,705,614 to Juttner et al; U.S. Pat. No. 2,715,430 to Lindeman; and U.S. Pat. Nos. 4,019,552 and 4,154,279 to Tsuruta.
One of the major drawbacks of these various approaches is that they generally require a substantial amount of operator attention to achieve the desired air pressure. For the most part, these systems require an operator to activate an inflate or deflate switch and then continually monitor an air pressure gauge until the desired pressure is reached at which time the operator must deactivate the switch. Moreover, no provision was made for accurately and automatically maintaining the tire pressure once initially set by this operation. These problems are especially acute when the vehicle is under enemy attack where the soldier's time could be much better spent in defending himself than in watching gauges.
Equally unsatisfactory is the prior art approach to controlling the inflate/deflate valve. In the past only one control valve was generally used which gradually opened or shut depending on the pressure differential between the desired and actual pressure within the tires. For example, as the pressure differential decreased the valve gradually shut off until there was equilibrium. Unfortunately, this technique unduly increased the inflate/deflate cycle time which is extremely important under battle conditions.
A simple, yet reliable seal for the air passageway between the rotating and nonrotating members of the wheel assembly has been difficult to obtain in the past. Many of the prior art approaches have been relatively complex and hard to assemble. Commonly used air seals with one or more generally vertically extending sealing flaps may have a tendency to lift up from their surfaces under high pressure thereby destroying the integrity of the seal. Still other seal designs were located outside of the bearings and exposed to adverse environmental conditions reducing their useful lives.
Many of the internal air feed wheel assemblies cut into load bearing members (e.g. axles, shafts) to form the air passageways. This unfortunately reduces the strength in these members. Some of the prior approaches also required relocation of the bearings from their originally designed position thereby often necessitating redesign of related parts at additional cost.
Many of the military vehicles currently in use still have many years of useful lives left or they are still in production. In some instances it would be desirable to modify these vehicles at low cost to include an automatic tire inflation system. However, many of the prior art approaches are specifically designed for a particular application and cannot easily be incorporated into conventionally used military vehicles such as M809, M44A2 and M939 military trucks.
The present invention is directed to solving one or more of the problems set forth above.